Definition of hydrogen service

Definition of hydrogen service

Definition of hydrogen service

Normally hydrogen partial pressure greater than 100 psia will be considered as hydrogen service regardless temperature. However, I saw a spec saying temp also to be above 400F then it will be as hydrogen service. That means if hydrogen partial pressure is 2000 psia and the design temp is only 300F, it is not considered as hydrogen service such that many special mechanical requirements are not required. Well, that will save a lot of cost. Do you agree temp shall be involved to define hydrogen service ? (Reference: Neilson curves)

RE: Definition of hydrogen service

hi
Hydrogen service may stand for "hydrogen containing environment" which may lead to safety concern whatever the temperature is.
if we talk about "hot hydrogen service" for which HTHA can develop, there is no universal definition : users have dissimilar definitions for hot hydrogen service. In my opinion, hot hydrogen service (with HTHA concerns) should be understood as the (temperature ; H2 partial pressure) ranges for which additionnal requirements are necessary to ensure resistance of the material to HTHA.
We use {ppH2 > 50psi when T > 400F} or {ppH2 > 800psi when T > 350F}, which are the limits beyond which CS should at least be PWHT or LAS selected.
API does not define H2 service and only provides so called Nelson curves.
The new Nelson curve (API RP941) for non-PWHT carbon steel could be understood as the API definition of hydrogen service. You must then acknowledge this definition or not, or define your own limits based on feedbacks and other documentation (for example CSB report on Tesoro Anacortes accident).

regards

RE: Definition of hydrogen service

I have very limited experience in hydrogen service equipment (so take the below as anecdotal) but based on what's been mentioned already it may be worthwhile reading Section 5.1.3.1 of API 571 and API 941.